Bowling foul indicator



Dec. 29, 1953 W. S. SWIFT BOWLING FOUL INDICATOR Filed March 25. 1950 Signals Currenf durce PLUG BYCZ L Patented Dec. 29, 19.53

BOWLING' FOUL INDICATOR Walters. Swift, East Rochester, N. Y., assigner to Edward J Doyle, RochestexgvN. Y.

.Application Marchas, 195o, seri-a1 No. 151,960

c1.,.27s,5o)

` 9 Claims.

This invention relates to a' foul indicator or detector iorbow'ling alleys.

Many attempts Ihave been made to provide automatic foul indicators vfor bowling alleys, but most of the prior vconstructions are relatively complex, due at least in part to the designers attempt to provide a complete foul indicator which will register Ievery possible type of foul. Many of'theseprior'fou'l indicators not only have complex, costly, and Vhard-to-service electric circuits, but also lhavebeen ditlcult and expensive to install, requiringin-atleast some instances the rather extensive mutilation of the bowling alley, so that-thealley'is at least disgured if not'actually left in a damaged condition if it is desired to remove the foul indicator permanently.

IIt is, accordinglyanfobject of the present invention to provide `a foul indicator or detector which is simple and inexpensive tobuild and to install and to service or maintain in operative condition, and which requires no substantial mutilation of the 4bowling alley in yconnection with installation of lthefoul indicator, rso Ythat the alley remains entirely sightly and suitable for use leven if itis desired to 'remove the indicating mechanism.

Another object of the invention is the provision of a foul'indicator so designed'andconstructed asto give lan indication of those fouls or types of fouls which'most commonly-occur and which are most dicult to detect by normal visual inspection, the 'apparatus being 'so designed that it does not ordinarily respond to orgive an indication of the comparatively rare types of fouls, which are, however, quite obvious to the player himself and to others observing the game, so that they are easily Vdetected by casual visual inspection. This exclusion of the less frequent and more'obvious ftypes of fouls `from the scope of the apparatus enables a'great simplification of the apparatusascompared with many of the prior foul indicators.

A 'further object -ofthe invention is theiprovision of va foul 'indicator in which theelectric circuit parts which are most likely vto A'need servicing or attentionfof any kind,are encasedk within a smallylight, eand compact box orfcasing of'a portable nature; .whichissimplyplugged into the permanently fixed parts rofthe electric circuit, so that when anything .goes wrong withthe apparatus,l it 4`canfin;mostcases be remediedv practically instantly `byunpluggingthe-boxfor casing containing the electronic circuit `parts :and plugging in-a duplicatefbox, whereupon the rst boxmay be takenfbytheserviceman vto his ,own

Jie

shop'where itmay be worked upon at leisure and Jth greater'eiiciency than could be done if the electronic circuits had Ato be serviced at the bowling alley location.

A still further object of the invention is the provision of a bowling foul indicator operating upon electronic principles, so designed and constructed as to eliminate or Vgreatly reduce the possibility of interference or faulty operation as a result of other electrical apparatus in the neighborhood, such as 4electric motors, or neon signs.

These and other desirable objects are accomplished by the construction disclosed as an illustrative embodiment of the invention in the following description and in the accompanying drawings forming apart hereof, in which:

Fig. 1 is a fragmentary planof the portion of a bowling alley adjacent the foul line, with the present 'inventionfapplied thereto, the invention being illustrated partly in schematic diagram;

Fig, 2 is a transverse vertical section through a bowling alley at the foulline, showing parts of the present invention; and

Fig. 3 is a schematic wiring diagram of the electric circuit parts of the present invention.

The samereference numerals throughout the several views indicate-the same parts.

Referring now-'to Eigsl and 2 of the drawings, there is shown a fragment of the usual bowling alley Il 'having the usual gutters I3, and a foul line l5 marked on the alley by means of a line of paint or other an inch) vonto or footis very quickly withdrawn yfrom this posiillegally crossed'theifoul line. Itis fouls of this kind which ,the presentapparatus is intended to indicate.

A Other` fouls of aless frequent kind are those in which, forlexample, -th-e-player may'lose 4his floor beyond the foul line. Or he may, to regain his balance, take a long stride iorwardly and step on the alley iloor considerably beyond the foul line. Fouls of this nature are not intended to be ordinarily detected by the present apparatus (which permits a great simplification of the apparatus) but the player himself is almost always perfectly conscious of the foul which he has committed, and it is glaringly apparent to the onlookers by even casual observation. Hence there is not the same necessity for apparatus to Y indicate automatically fouls of this nature, asv

there is for fouls of the more frequent but less easily detected types previously mentioned.

in order to detect and indicate fouls of the types falling within the scope of the present apparatus, each alley is provided at one side, at the foul line, "with light projecting means such as the casing 2! having a light bulb 23 therein, and provided with a suitable slit or lens or both, for optically directing and controlling a beam of light to project it across the alley exactly in the vertical piane oi the foul line l5 and spaced a slight distance above the alley floor, for example with the center of the beam about 3A; of an inch above the alley floor, the projected beam or" light being indicated diagrammatically by the dash line 2l. At the opposite side of the alley, in direct alinernent with the foul line i5, the beam of light is received by a phototube 3|, conveniently of known type 921. So long as the beam of light from the projector 2l falls on the phototube 3l, the phototube is conductive to a high degree, but when the players foot or other obstruction interferes with the beam of light from the projector 2i reaching the phototube 3|, the phototube is conductive to a lesser extent or not at all. It is this variation in electrical conductivity or the phototube, in response to the incidence or exclusion of the light beam 2l', which initiates operation of the indicating mechanism. Although a beam of light has been mentioned. it will be understood that a beam of so-called invisible light or infrared radiation falls within this term as herein used.

Referring now to the diagrammatic representationV at the right hand side of Fig. 1, the indieating mechanism comprises, in a very general way, a source of current indicated diagrammatically at 35, signals or indicators operated by such source of current and indicated diagrammatically at S7, and electronic control mechanism indicated diagrammatically at Se for controlling the operation of the signals 3l' in response to variations in conductivity of the phototube 3|. The signals 3'! may be oi any desired kind and number: for example, an audible signal such as a bell or buzzer, and a visual signal such as a light. In addition, the present mechanism includes a plug connection indicated diagrammatically at Lil, through which plug connection the control mechanism 39 is electrically attached to or detached from the phototube 3|, the current source 35, and the signals 37|. rlhis plug connection may be instantly connected or disconnected, so that if any services or repairs are needed with respect to the control parts, the entire control mechanism 39 may be unplugged and taken away as a unit for servicing at a shop where all servicing facilities are conveniently available, and may be replaced by a duplicate unit so as not to interfere with the operation of the bowling alley.

Reference is now made to Fig. 3 of the drawings, which shows diagrammatically the construction of the control unit and associated parts. The

separable or detachable plug 4| is here indicated, and it may conveniently be in the form of a 7 wire or 7 prong plug of conventional design. The source of current 35, the phototube 3l, and the signals and certain associated parts are indicated in Fig. 3 as being to the left of the plug 4|. The control unit comprises those parts to the right of the plug all, in Fig. 3, and it may be stated at this pointthat this entirecontrolunit is of such simplicity and compactness 'that the box or casing 39 holding the control unit parts may be of a size no larger than about 3 X 4 X 5 inches, weighing no more than about 21/2 pounds. With these gures in mind, it is seen that portability of the control unitv is real rather than theoretical, and it is a very easy matter for the bowling alley operator, when operating a number of alleys equipped with this invention, to keep a few extra control units on hand. If anything appears to be wrong with the operation of the foul indicator on any one alley, the operator simply taires one of the spare control units and plugs it into the circuit in place of the control unit which appears to be out oi order, as easily as or perhaps even quicker than changing an ordinary light bulb. Then the alley operator calls his electronic service man at leisure and gives him the faulty control unit which was unplugged from the circuit, to be tested and repaired in due course and brought back to the alley operator ready for use in the event of any future troucle with any control unit of any alley.

Referring new to the details of the control unit (Fig. 3) the unit comprises a thyratron tube 45, such for example as a type 2050 tube. The anode of this tube is connected by the wire QS to one side of a relay 5|, and through the relay to the wire 53 leading (through the separable plug 4|) to the source of current 35, and also to one side of the visual signal |9| and one side of the audible signal ist. The current source 3'5 may conveniently be any source of volt alternating current, such as the ordinary electric lighting circuit. The relay 5| may conveniently be a conventional type SUl'D. A capacitor 55, having a capacity of 1 mid., is placed in parallel across the relay 5|.

The relay has an armature 5l which is normally urged by a spring 59 in a direction away from the relay coil, or upwardly when viewed as in Fig. 3. rfhis armature 5l is mechanically connected, as indicated diagrammatically by the dash line to the movable contact members or switch arms of a four pole double throw switch, forming in effect four switches whose switch arm pivots are indicated at 6|, li, 8|, and 3|, respectively. .The respective switch arms are engaged with the respective contacts. 62, l2, 32, and 92 when no current is ilowing in the relay 5|, so that the armature 5l is in its upper position, and are respectively engaged with the other contacts 553, 73, 83, and S3 of these respective switches when suicient current is flowing in the relay 5| to pull the armature 5l down against the action of the spring 59.

The switches t! and 'l on their xed sides, are connected to each other by the wire lill, in which is interposed a capacitor |93 having a capacity of 0.15 mfd. From the contact 62 of the switch Bi, a wire |05 leads through the resistor |91 having a value of 22 megohms, to the junction point |09, whence a wire leads through the plug 4| to the cathode of the phototube 3|. From this same junction point |69, a wire ||3 Aleads through a fixed resistor having a value of 1.0 megohm to the first grid .or control .grid of the tube 45.

A branch |2i leads from the wire ||3 through a resistor |23 with a value of about 2.2 megohms, to the cathode of the tube 45. A capacitor |25 with a value of about 0.05 mid. is connected in parallel with the resistor |23. Another branch |21 leads from the wire ||3 through a capacitor |29 having a value of about 0.03 mfd., to a mid point tap lS oi the secondary |33 of the transformer |35.

The other side of the current source 35 (that is, the side which is not connected to the wire 53) is connected to a wire |43 which leads through the separable plug 4| and thence, by means of Various branches, to the relay switch parts 83, 12, 8|, and 9|, as well as to the right end of the primary |49 or the transformer |35, the rightend of the secondary |33 cf the same transformer, and to the cathode and the grid of the tube The left end of the primary winding |49 is connected by the wire 53 to the rst mention-ed side of the current source 35. The filament of the tube 45 is supplied with heating current at 6.3 Volts by a connection |45 to the right hand end of the secondary winding |33 and a connection to the center tap 3| thereof. The full secondary winding voltage of 12.6 volts is supplied from the left end of the winding |33, through a wire 29|, to the coil 263 of an oil dash pot relay, the other side of this coil being connected by the wire 2535 to the switch Contact 92.

A branch of the wire 53 leads to the selenium rectier |53, from the opposite side of which a wire 135 leads to the switch contact 13 of the switch 1|. Also a branch of this wire |65 leads through the resistor |1| to a wire |12 which, after passing through the separable plug 4|, goes to one end oi a potentiometer |13. The other end of the potentiometer is connected by a wire |14,

again passing through the separable plug 4|, to one end of the resistor |15, the other end of which is connected to a branch of the current source line |43. Conveniently the resistor |1| has a value of L17,000 ohms, the potentiometer |13 a value of 20,000 ohms, and the resistor |15 a value of 33,060 ohms. A capacit-or |11 having a Value of 8 mfd. is connected between those ends of the resistors iii and |15 which are remote from the member 13, this capacitor thus being connected, in effect, between the wires |43 and |65. The sliding or adjustable Contact 8| of the potentiometer |13 is connected by a wire |83 to the anode o1" the phototube 3|.

The signals or indicators comprise preferably a visible signal such as the electric light 19| and an laudible signal such as the bell or buzzer As already mentioned, one side of the light |3| and audible signal |33 is connected directly to the current source line wire 53. The second side of the audible signal |33 is connected by a wire |95 passing through the separable plug 4| to the contact 82 of the switch 8 The second side of the visible signal 9i is ccnnected by the wire l 91 passing through the separable plug fil to one side of the armature switch |89 of the oil dash pot relay 203 above mentioned, the other side of this relay switch being connected to the current line wire 43.

The operation is as follows:

The selenium rectier |63 provides a direct current voltage of approximately 155 volts positive on the wire |35 and on the adjacent end of the resistor |1I. The elements |1|, |13, and |15 act as a voltage divider circuit, impressing a posisecond grid or shield tive voltage, through 'the Wire |83, on the anode of the phototube 3 l` The potential of such positive voltage on the anode is determined by the resistance values of the elements 11| and |15, and by the adjustment of the contact |8| on the potentiometer |13, and this determines, in part, the length of time that the tube 4'5 remains inoperative after a foul has been committed. The potentiometer is preferably adjusted so as not to exceed approximately volts on the anode, if the phototube 3| is a tube of the kind or type known in the industry as a 921 tube.

The transformer |33, |35, |49, operating directly from the main alternating current supply line, provides the usual 6.3 volts to the heater iilament, through the leads |3| and |45, and through the wire 23| it supplies 12.6 volts to the dashpot relay 203. In addition, through the capacitor |29 and wire |21, the secondary of this transformer applies negative potential to the rst or control grid of the tube 45, with respect to the positive potential impressed on the anode. To attain this result, correct phasing of the circuit from the secondary of the transformer to the grid, as compared with the circuit connections between the primary of the transformer and the anode, is essential. The matter of phasing is well understood by those skilled in the art, and it will be apparent that if the connections do not give the desired phase relationship, the connections to either the primary oi the secondary of the transformer may simply be reversed and the correct phase relationship Will then result,

This system is designed to function with the tube 45 normally conducting when the beam of light 21 is falling upon the cathode of the photocell 3|, and no signal of a foul is produced while the tube 45 is conducting. When the beam of light 21 falling on the photocell is interrupted for more than a predetermined length of time sufficient for passage of the bowling ball, the tube 45 becomes non-conducting and then the signals |9| and |93 are operated.

At the height of the light beam 21 above the surface of the alley (preferably about A of an inch) the maximum diameter of the bowling ball is considerably above the elevation of the light beam and so as the bowling ball travels down the alley, the light beam intercepts only a relatively short chord of the circular outline of the ball, rather than the full diameter thereof. Even when the ball is propelled rather` slowly down the alley, the intercepted chord will pass the light beam in considerably less than a fifth of a second, frequently in as little as a tenth of a second. Yet if the bowlers foot is placed over the foul line and intercepts the light beam, a person with normal reflexes cannot withdraw the foot in less than a iifth of a second, and ordinarily it taires a substantially longer time for withdrawal. Hence the present arrangement is designed with a time delay or lag of approximately one-iifth of a second, so that no indication of a foul is given if the light beam to the photocell is interrupted for a iifth of a second or less, but a signal of a foul is given when the light beam is interrupted for more than a fifth of a second.

With the beam of light falling on the phototube 3| and with the tube 45 in the conducting or operating condition, current iiows through the anode circuit or plate circuit of the tube 45, and through the Wire 49 and the relay 5|, thus operating the relay and pulling the armature 51 against the force of the spring 5S, thus pulling all of the switches 6|, 1|, 8|, and 9| to the positions indicated in Fig. 3. In these positions, the switches 8| and 9| are open so that the signal indicators |9| and |93 do not operate. Also, in this position, the wire |65 through the closed switch 13, 1| impresses the full rectied positive potential of approximately 155 volts from the rectier |53 on one side of the capacitor |03, the

opposite or negative side of the capacitorV being connected through the switch contact 03 with the line |33.

So long as the light beam continues to fall on the phototube 3|, the phototube conducts the current supplied by the potentiometer |13 through the wire |83, and the positive current is thus supplied through the Wire from the phototube to the wire ||3 leading to the grid of the thyratron tube 45, so that the tube 45 remains in its operating or conducting condition. If the light beam to the phototube 3| is momentarily interrupted for a very short time (less than about one-fifth of a second in the present embodiment) so that current ceases to flow through the phototube, the thyratron tube 45 still remains conducting, however, due to the Voltage stored in the capacitor |25. It is the values of the elements ||1, |23, and |25 which determine the length of time that the tube 45 will continue to conduct, after the light beam to the phototube 3| is interrupted. This time lag, or length of time of continued operation, may be adjusted or varied by appropriate changes in the values of these elements ||1, |23, and |25.

If the light beam to the phototube 3| continues to be interrupted and the phototube thus continues to be non-conducting for more than the set or predetermined length of time (approximately one-fth second in the present preferred embodiment) so that the grid of the tube 45 becomes suiiciently negative (due to the negative potential supplied by the transformer secondary |33 through the wire |21 and capacitor |29) then the tube 45 ceases to conduct. As soon as the current through the plate circuit 49 of the tube 45 stops, the relay 5| opens under the action of the spring 59, and the movable switch arms of all of the switches 6|, 1|, 8|, and 9| are shifted from the lower contacts to the upper contacts, when viewed as in Fig. 3. The switches 3| and 9| thus closing to the contacts B2 and 92, respectively, complete the circuits to set the signals |9| and |93 in operation. In the case of the visible signal |9|, the closing of its switch 9| to the contact 92 completes the cocking circuit of the dash pot relay 203, so that the current furnished by the transformer secondary |33 iiows through the relay coil 203, attracting the relay armature |99 to close the relay armature switch to light the signal light |9|. The oil dash pot connected to the relay armature keeps this relay armature switch closed for about ten seconds after current stops flowing through the relay coil 203, so that the signal light |9| remains lit for a minimum of ten seconds, insuring adequate observation time. Oil dashpot relays of this kind are well known and are obtainable on the market, the details of construction of the dashpot relay forming no part of the present invention.

Simultaneously with the closing of the switches 3| and 9|, the shifting of the switch arms of the switches and 1| to the contacts 62 and 12, respectively, serves to connect the positively charged side of the capacitor |03 to the line |43,

. and connect the negatively charged side of the capacitor |03 through the resistor |01 to the wires |05 and ||3 and the'grid of the tube 45. Hence, for the length of time required for the negative charge to leak off from the capacitor |03 through the resistor |01, the grid of the tube 45 will'remain negative and the tube will not conduct, even though the interruption of the light beam may have ceased and the phototube may again be conducting. It is ordinarily desired to keep the bell |93 operating for approximately two seconds, to make sure that it is heard by the player and onlookers, and so the values of the elements |03 and |01 are chosen so as to keep the grid of the tube suiciently negative to prevent the tube from conducting, for about two seconds.

Assuming that the interruption of the light beam 21 has ceased and that the light beam is again falling on the phototube 3|, the phototube 3| is again conducting and is supplying positive potential to the grid of the tube 45, bucking the negative potential from the capacitor |03. When the effect of the negative potential from the capacitor |03 has iinally been overcome by leaking oii through the resistor |01, in about two seconds as above explained, the grid of the tube 45 will become insufficiently negative to prevent electron iiow, so that the tube again becomes conducting, whereupon current again begins to flow through the relay 5| in sufficient quantity to operate the relay, pull the armature 51 down against the action of the spring 59, and shift all four of the switches 0|, 1|, 8|, and 9| back to the positions shown in Fig, 3, opening the switches 9| and 9|, thus immediately stopping the operation of the bell, stopping the flow of current through the dashpot relay coil 203 so that the light |9| will go out about 10 seconds later, and shifting the switches 9| and 1| so that the capacitor |03 again becomes charged ready for the next foul indication.

The length of time that the signal |93 continues to operate, after being set into operation, depends partly upon the values of the elements |03 and |01 and partly upon the voltage impressed on the phototube by the potentiometer |13 and circuit |33. Hence this length of time can be adjusted by varying either the element |03 or the element |01, or (usually more conveniently) by adjusting the slide |3| on the potentiometer |13, to vary the impressed voltage on the phototube.

The second grid of the tube 45 is a shield grid, and is not essential, but a tube of this kind usually gives more satisfactory operation if a shield grid is employed, as well understood by those skilled in the art.

The resistor |23 has the effect of limiting voltage surges which might otherwise be transmitted to and damage the phototube 3|. The resistor il serves to isolate the grid of the tube 45, and as a grid load resistor, and it should be placed as close to the tube as possible, preferably being mounted right on the base of the tube.

It should be understood that the voltages, resistances, and capacities of various parts of the circuit which have been mentioned'above are given merely as illustrative examples of a satisfactorily operating embodiment. rfhose skilled in the art will readily understand that all of such factors may be changed without departing 1n any way from the principles or" operation as herein disclosed. Moreover, when it is stated above that the values of a given resistor or capacitor will control a given function or operation, 1t is meant that such values will effect the maior control of such function or operation.

9 lt is realized, of course, that the functioning of the Vapparatus is also dependent partly on lthe internal or inherent capacitance and resistance 'of the various parts of the circuits, including the tube itself.

It is pointed out that the present system in which the tube i5 is normally7 in a conducting condition, and becomes non-*conducting only when a foul occurs, has important advantages v-over the usual prior system in which an electronic tube is normally non-conducting and becomes conducting only when a foul occurs. An electronic tube of the type 2050 which is here vmentioned as an illustrative example, is rather unstable in operation, and it may easily happen that when the tube is non-conducting, it may nre or become conducting under the influence of an extraneous electrical disturbance in the neighborhood, such as produced by operation of 'an electric motor, a doorbell, or a neon sinn. Hence if the circuit were designed so that the tube would be normally non-conducting, the operation of extraneous electrical appliances in the vicinity might cause the tube to fire with the result of indicating a foul when none actually occurred. But in the present system, the tube is normally operating in a conductive condition, in which condition it is not subject to appreciable inuence by extraneous electrical appliances in the vicinity. It is only occasionally and only for 'relatively short periods of time, that the tube 45 will be in a non-conducting condition. when a foul has been committed, and thus the time during which the tube is Vulnerable or susceptible to influence by extraneous electrical appliances is greatly reduced as compared to the time it would be vulnerable if it operated the other way.

Another advantage of the present system is lthat when the electricity is turned on at the beginning of the ld ays opera-tion, the Warm-up period oi the tube 45 (usually about 10 seconds) serves as a test of the correct functioning or the equipment. When the current is iirst turned on, the cold tube e is, of course, non-conducting, so the light and bell signals I9! and |93 immediately begin to operate. If the various circuits are operating correctly. the bell will cease to operate when the tube has warmed up to conductive condition, the signal light will go out about ten seconds thereafter, the delay in this case being due to the action of the oil dashpot relay.

Still another advantage of the present arrangement is that the tube is not damaged by turning on the anode current immediately when the filament is turned on. Manufacturers of thyratrons usually recommend a warm-up period of ten seconds before anode voltage is applied. In the present construction, however, anode voltaffe is applied to the cold tube. this being` safe because the low current demand (only about 8% of the maximum rated current) prevents dama're to the tube, as substantiated by tests both in the laboratory and in the field.

It is seen from the foregoing disclosure that the above mentioned objects of the invention are admirably fuiiled. It is to be understood that the foregoing disclosure is given by way of illustrative example only, rather than by way of liinitation, and that without departing from the invention, the details may be varied within the scope of the appended claims.

What is claimed is:

1. A bowling foul indicator including a :phototube, means )for projecting a beam of light .adja- 'iii cent la foul line of a bowling alley and toward said phototube in vposition to be intercepted when a foul is committed, a vacuum tube having a cathode, an anode, and a grid, means for supplying positive potential to said phototube and through said phototube to the grid of said vacuum tube to maintain said vacuum tube in conducting con-dition While current iiows through said phototube, electric signal means including a visible signal, an anode circuit operatively connected to said vacuum tube and normally having a flow of current therein, a relay switch in said anode circuit, means operatively connecting said electric signal means to relay switch in such manner as to initiate operation of said signal means when current ceases to i'iow in said anode circuit, circuit means including a resistor and a capacitor in parallel with each other and 'operaively connecting said cathode and said grid of said tube to each otherl to maintain the anode circuit of said tube in conducting condition for a relatively short time interval after light ceases to fall on said phototube, sufficient to permit a ball to pass through said beam or" light without causing a foul indication, a portable casing containing said vacuum tube and relay switch, said phototube and said signal means being mounted externally of said portable casing, and separable plug connection means associated with said portable casing and interposed in the electric circuits leading' from the parts within said portable casing to the parts externally thereof, said portable casing being relatively small and containing all amplifying circuit parts so that all of suoli amplifying circuit parts maybe removed from a bowling alley for convenient inspection and servicing by disconnecting said separable plug and removing said portable casing,

2. An indicator as defined in claim l, in which said means operatively lconnecting said Visible signal to said relay switch includes a time delay relay1 of the dashpot relay type to keep vsaid visible signal in operation for an interval of time after reestablishment of flow of current in said anode circuit.

3. A bowling foul indicator including a phototube, means for projecting a beam of light adjacent a foul line of a bowling alley and toward said phototube in position to be intercepted when a foul is committed, a vacuum tube having a cathode, an anode, and a grid, means for supplying positive potential to said phototube and through said phototube to the grid of said vacuum tube to maintain said vacuum tube in conducting condition while current ows through said phototube, electric signal means, anode circuit operatively connected to said vacuum tube and normally having a now of current therein, a relay switch in said anode circuit, means operatively connecting said electric signal means to said relay switch in such manner as to initiate operation of said signal means when current ceases to ow in said anode circuit, a capacitor, and capacitor circuit connections leading through said relay switch in such manner that when current is normally flowing in said anode circuit, said capacitor is charged, and when current is not owing in said anode circuit, the negative side of said capactior is connected to the grid of said vacuum tube to maintcin said grid suilciently negative to prei'ent ow of current in said anode circuit for a predetermined minimum time after cessation of flow of current in said anode circuit.

Ll. An indicator as dened in claim 3, further including a resistor in said capacitor circuit connections leading from said capacitor to said grid.

5. An indicator as dened in claim 4, further including a source of alternating current, and a current rectiier, said means for supplying BOS- tive potential to said phototube and for charging said capacitor including circuit connections from said rectier to said phototube and to said capacitor, respectively.

6. An indicator as defined in claim 5, in which said vacuum tube, relay switch, capacitor, resistor, and rectiiier are all mounted in a single portable casing and are electrically connected to said source of current, phototube, and signal means through a multiple-wire separable plug.

7. A bowling foul indicator control unit including a portable casing, a multiple-wire plug having separate connection terminals adapted to be connected to a source of alternating current, to a phototube, and to electric signal means, and electric control parts within said casing, said control parts including a vacuum tube having a iilament, a cathode, an anode, and a control grid, a multiple relay switch having an operating coil, a transformer, a rectier, a capacitor, a resistor,

and circuit connections operatively connecting said cathode and the input side of said rectier and one side f the primary winding of said transformer to the plug connection for one side of said source of current, operatively connecting one side of the operating circuit of said relay switch and the second side of said primary winding to the plug connection for the second side of said source of current, operatively connecting the anode of said vacuum tube to the second side of the operating circuit of said relay switch, operatively connecting the positive rectied side of said rectiiier to the plug connection for the anode of the phototube, operatively connecting the control grid of the vacuum tube to the plug connection for the cathode of the phototube, operatively connecting the positive rectified side 0f said rectifier to one side of said capacitor and the negative side of said capacitor to the plug connection for the iirst side of said source of current through said relay switch when the latter is in the position it assumes when current is flowing through the operating circuit of the relay switch, operatively connecting the positive side of said capacitor to the plug connection for the rst side of said source of current and the negative side of said capacitor to one side of said resistor through said relay switch when the latter is in the position it assumes when no current is flowing through the operating circuit of the relay switch, operatively connecting the second side of said resistor vto the control grid of said vacuum tube, operatively connecting the secondary winding of said transformer to the lament of said vacuum tube, and operatively connecting the plug connection for one side of said source of current to the plug connection for said signal means through said relay switch when the latter is in the position it assumes when no current is flowing through the operating circuit of the relay switch.

8. A construction as dened in claim 7, further including a time delay relay mounted in said casing and operatively interposed in the circuit connections of said signal means to keep said signal means in operation for an interval of time after said relay switch assumes its controlcurrent-owing position.

9. A construction as dened in claim 8, in which said time delay relay is an oil dashpot relay.

WALTER S. SWIFT.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 2,214,274 Glendenning Sept. l0, 1940 2,417,092 Smith Mar. 11, 1947 2,425,255 MacLagan Aug. 5, 1947 2,425,258 MacLagan Aug. 5, 1947 2,455,909 Smith Dec. 7, 1948 hq,... wam- 

